1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to arc fault and/or ground fault circuit interrupters providing a cost-effective user interface to selectively enable forms of protection and/or configure protection settings. The invention also relates to methods of cost-effectively enabling forms of protection and/or configuring protection settings of circuit interrupters.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
An arc fault circuit interrupter (AFCI) is a device intended to mitigate the effects of arc faults by functioning to deenergize an electrical circuit when an arc fault is detected. Non-limiting examples of AFCIs include: (1) arc fault circuit breakers; (2) branch/feeder arc fault circuit interrupters, which are intended to be installed at the origin of a branch circuit or feeder, such as a panelboard, and which may provide protection from ground faults and line-to-neutral faults; (3) outlet circuit arc fault circuit interrupters, which are intended to be installed at a branch circuit outlet, such as an outlet box, in order to provide protection of cord sets and power-supply cords connected to it (when provided with receptacle outlets) against the unwanted effects of arcing, and which may provide protection from line-to-ground faults and line-to-neutral faults; (4) cord arc fault circuit interrupters, which are intended to be connected to a receptacle outlet, in order to provide protection to an integral or separate power supply cord; (5) combination arc fault circuit interrupters, which function as either a branch/feeder or an outlet circuit AFCI; and (6) portable arc fault circuit interrupters, which are intended to be connected to a receptacle outlet and provided with one or more outlets.
Arc faults can be series or parallel. Examples of a series arc are a broken wire where the ends of the broken wire are close enough to cause arcing, or a relatively poor electrical connection. Parallel arcs occur between conductors of different potential including, for example, a power conductor and a ground. Arc faults have a relatively high impedance. Thus, a series arc results in a reduction in load current and is not detected by the normal overload and overcurrent protection of conventional protection devices. Even the parallel arc, which can draw current in excess of normal rated current in a circuit, produces currents which can be sporadic enough to yield RMS values less than that required to produce a thermal trip, or at least delay operation. Effects of the arc voltage and line impedance often prevent the parallel arc from reaching current levels sufficient to actuate the instantaneous trip function.
During sporadic arc fault conditions, the overload capability of a conventional circuit breaker will not function since the root-mean-squared (RMS) value of the fault current is too small to activate the automatic trip circuit. The addition of electronic arc fault sensing to a circuit breaker can add one of the elements required for sputtering arc fault protection-ideally, the output of an electronic arc fault sensing circuit directly trips and, thus, opens the circuit breaker. See, for example, U.S. Pat. Nos. 6,710,688; 6,542,056; 6,522,509; 6,522,228; 5,691,869; and 5,224,006, and U.S. Patent Application Publication No. 2005/0017731, all of which are incorporated herein by reference.
In ground fault circuit breakers, for example, an electronic circuit typically detects leakage of current to ground and generates a ground fault trip signal. This trip signal energizes a trip solenoid, which unlatches the operating mechanism, often through deflection of the armature of a thermal-magnetic trip device. Ground fault circuit breakers include both Class A (e.g., ground fault current of about 5 mA for people protection) and equipment protective devices (e.g., ground fault current of about 30 mA; of about 20 to about 100 mA).
AFCI functionality in the field of residential circuit protection is known, but to date, cost considerations have caused the provision of AFCI functionality in residential settings to remain uncommon.
Circuit protection devices are used in commercial settings where a greater degree of operator input in selecting forms of protection and protection settings are commonly provided. Relatively large electrical loads and a host of more stringent safety standards have resulted in costs being less of a factor than in residential settings such that more complex circuit protection devices having more features are commonplace in commercial settings. Adding to the complexity and costs of circuit protection devices employed in commercial settings is the provision of control mechanisms through which GFCI and/or AFCI functions may be selectively enabled and sensitivity levels for such functions may be set.
In more recent years, with the technological progress resulting in ever more uses for electricity, the amount of electrical power required in residential settings has markedly increased. Residential structures now employ greater quantities of electric circuits, and many of these electric circuits are of greater capacity. As a result, it has become ever more desirable to more widely employ GFCI and AFCI functionality in residential settings. However, costs and complexity remain issues that continue to slow the introduction of such functionality into a residential setting.